In the field of semiconductor manufacture, it is often useful or necessary in practice to join and/or remove films or layers of semiconducting or insulating material. On the one hand, it may be desired to prepare final stacked structures containing a three-dimensional design of electronic, photovoltaic and/or optoelectronic elements. On the other hand, thin films of high purity material and high crystalline quality may be appropriately handled on support substrates, and it is necessary to dispose of effective means for transferring these films from initial to final support substrates.
Moreover, some kinds of semiconducting materials may not be available as bulk or free-standing substrates and must be handled on support substrates, despite problems of lattice mismatch and/or thermal expansion coefficient that may arise. Methods are needed for removal of the functionalized semiconducting material layer from its support.
In the area of functionalized semiconductor layers, such as silicon layers for example, it is also useful to have available a method enabling layer transfer. Indeed, the functionalization of such semiconductor layers may involve electronic circuits, photovoltaic elements (containing, for example, a Ge seed layer, and a triple junction active layer), and/or optoelectronic elements. Being able to expose, manipulate and bond with relative ease both “front” and “back” faces of semiconductor layers enables functional elements to be introduced when the semiconductor layer treated is on a supporting substrate which allows a certain type of functional modification, and those functional elements to be occluded and then re-exposed as later required. Thus, electronic circuits may be introduced on one face of a thin layer on an initial support substrate favorable for this functionalization step, and then the exposed and functionalized “front” surface may be bonded to an intermediate substrate. The removal of the initial substrate support enables other circuits to be prepared on the “back” face of the functionalized thin layer. The exposed “back” face may be further transferred, for example, to a support adapted to the operation of the functionalized centers created, for example, for heat dissipation.
Furthermore, the group III-V materials such as InGaAs, InP or InAlAs are very useful for solar cell applications and III-nitride materials such as GaN, AlGaN or InGaN are of considerable interest in the semiconductor industry for use in light-emitting devices such as light-emitting diodes, laser diodes and related devices. GaN is a promising material for optoelectronic applications as well as for high frequency, high power electronic devices. It is important to be able to provide GaN or InGaN layers showing a low amount of crystal defects and a high quality surface.
It is of interest in these areas of technology to dispose of methods enabling III-V and III-N materials to be provided on a variety of surfaces and support materials. In techniques in which the III-V material is grown by epitaxy on a substrate surface, a high crystalline quality and appropriate lattice parameters of the growth substrate are necessary to enable sufficient quality III-V growth, restricting the choice of underlying seed support substrates for the III-V material.
In systems where it is foreseen to access the III-V layer by etching techniques, this may prove problematic and lead to degradation of the III-V material.
It is also of interest to be able to expose particular faces of III-N substrates. In effect, it is common for polar c-plane III-N material to have a specific atom surface termination such that one surface is terminated by the element from group III and the other surface is terminated by nitrogen atoms.
In all the above-related cases, methods for detaching or exfoliating thin films or layers, or a stack of them, from a substrate are needed. Moreover, there is also a need for performing such a detachment or exfoliation without destroying the substrate in order to recycle it for subsequent uses.
Document EP 0 858 110 discloses an exfoliating method for exfoliating a detached member, which is present on a transparent substrate with a separation layer therebetween, from the substrate, wherein the separation layer is irradiated through the transparent substrate with incident light so as to cause exfoliation in the separation layer and/or at the interface, and to detach the detached member from the substrate.
However, when irradiating the separation layer with a laser beam through a transparent substrate, made of sapphire (Al2O3), for instance, an undesired topology or defects are produced on the surface of the substrate on which the separation layer is formed. This surface topology can be of 30 nm.
In order to make the substrate reusable after irradiation and exfoliation, this surface topology must be removed. In view of the level of the surface topology, a significant thickness of the substrate must be removed, for instance, by polishing, after each irradiation and exfoliation. This considerably limits the recycling capacity of the substrate.
Moreover, the polishing of transparent substrates, such as sapphire or silicon carbide substrates, is generally long and expensive due to the hardness of the material of the substrates.